3-(4'-Bromobiphenyl-4-yl)tetralin-1-one of the formula IV is an useful intermediate for the production of rodenticides and clinical medicines. The compound IV is disclosed in U.S. Pat. Nos. 3,957,824 and 4,035,505 and J. Chem. Soc. Perkin I, 1190 (1976). Their two different methods for the production of a compound of the formula IV are shown in Scheme 1: ##STR1## The reaction of an alcohol of the formula V with phosphorus tribromide in method 1 (Scheme 1) provided a dehydrated product which had stilbene structure (4'-(4'-bromophenyl)stilbene) as a side structure as well as a desired product of the formula VI. In addition, the dehydrated product had also formed as a side product in alkylation step of bromide VI to a compound of the formula VII. Since the cyclization reaction of a compound of the formula VII underwent through decarboxylation, the high temperature was required in that step.
In method 2 (Scheme 1), the known process used the Reformatsky reaction in the first synthetic step for the production of a compound II. In that step the reaction was performed with a compound I, ethyl bromoacetate, and zinc in benzene under reflux. In their condition, the separation of the desired product from an unconsumed starting ketone I was not easy and gave low isolation yield. Dehydration reaction of a compound II was carried out with P-toluenesulfonic acid, providing a desired .alpha.,.beta.-unsaturated carboxylic acid VIII with an isomerized .beta.,.gamma.-unsaturated acid VIII which was not easily reduced to saturated carboxylic acid, as shown in Scheme 2: ##STR2##
In addition, it had a difficulty to perform the cyclization reaction of a compound VIIII, because the compound VIIII in solid form was not mixed homogeneously with polyphosphoric acid.
The present invention provides a new and improved process for the preparation of 3-(4'-bromobiphenyl-4-yl)tetralin-1-one IV. And this invention overcomes the technical and economical problems shown in disclosed patents above.